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Get a big gatorade bottle or a big water bottle. Or even a 2 or 3 liter coke bottle. Then get a scissor and poke a hole into the side of the bottle. Get some string and put it through the hole. Where the big hole is at the top of the bottle pull the string through it. Tape it with some duct tape. put some rocks on the back and front to weigh it down in the water. Put some bread in the bottle or/and beef jerky. They catch minnows and crayfish. When you are making the top of the bottle better, if you are, make a funnel of duct tape. so the the fish go in but it is too small to get it.
THIS WORKS!
Step 1Get the bottle
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i dont have a pic. But just get a gatorade bottle or a big water bottle.
You might also want to drill lots of holes onto the body to promote natural water flow within the trap. And also, perhaps changing the shape of the funnel opening. You can take your design cue from here traditional fish trap.
The body of a fish is narrowly shaped, such funnel design would allow you to trap small and larger fishes.
http://www.instructables.com/id/Soda-Bottle-Fish-Trap/